1. Field of Inventions
The present invention relates generally to medical devices that support one or more diagnostic or therapeutic elements in contact with body tissue and, more particularly, to medical devices that support one or more diagnostic or therapeutic elements in contact with bodily orifices or the tissue surrounding such orifices.
2. Description of the Related Art
There are many instances where diagnostic and therapeutic elements must be inserted into the body. One instance involves the treatment of cardiac conditions such as atrial fibrillation and atrial flutter which lead to an unpleasant, irregular heart beat, called arrhythmia.
Normal sinus rhythm of the heart begins with the sinoatrial node (or xe2x80x9cSA nodexe2x80x9d) generating an electrical impulse. The impulse usually propagates uniformly across the right and left atria and the atrial septum to the atrioventricular node (or xe2x80x9cAV nodexe2x80x9d). This propagation causes the atria to contract in an organized way to transport blood from the atria to the ventricles, and to provide timed stimulation of the ventricles. The AV node regulates the propagation delay to the atrioventricular bundle (or xe2x80x9cHISxe2x80x9d bundle). This coordination of the electrical activity of the heart causes atrial systole during ventricular diastole. This, in turn, improves the mechanical function of the heart. Atrial fibrillation occurs when anatomical obstacles in the heart disrupt the normally uniform propagation of electrical impulses in the atria. These anatomical obstacles (called xe2x80x9cconduction blocksxe2x80x9d) can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called xe2x80x9creentry circuits,xe2x80x9d disrupt the normally uniform activation of the left and right atria.
Because of a loss of atrioventricular synchrony, the people who suffer from atrial fibrillation and flutter also suffer the consequences of impaired hemodynamics and loss of cardiac efficiency. They are also at greater risk of stroke and other thromboembolic complications because of loss of effective contraction and atrial stasis.
One surgical method of treating atrial fibrillation by interrupting pathways for reentry circuits is the so-called xe2x80x9cmaze procedurexe2x80x9d which relies on a prescribed pattern of incisions to anatomically create a convoluted path, or maze, for electrical propagation within the left and right atria. The incisions direct the electrical impulse from the SA node along a specified route through all regions of both atria, causing uniform contraction required for normal atrial transport function. The incisions finally direct the impulse to the AV node to activate the ventricles, restoring normal atrioventricular synchrony. The incisions are also carefully placed to interrupt the conduction routes of the most common reentry circuits. The maze procedure has been found very effective in curing atrial fibrillation. However, the maze procedure is technically difficult to do. It also requires open heart surgery and is very expensive.
Maze-like procedures have also been developed utilizing catheters which can form lesions on the endocardium (the lesions being 1 to 15 cm in length and of varying shape) to effectively create a maze for electrical conduction in a predetermined path. The formation of these lesions by soft tissue coagulation (also referred to as xe2x80x9cablationxe2x80x9d) can provide the same therapeutic benefits that the complex incision patterns that the surgical maze procedure presently provides, but without invasive, open heart surgery.
Catheters used to create lesions typically include a relatively long and relatively flexible body portion that has a soft tissue coagulation electrode on its distal end and/or a series of spaced tissue coagulation electrodes near the distal end. The portion of the catheter body portion that is inserted into the patient is typically from 23 to 55 inches in length and there may be another 8 to 15 inches, including a handle, outside the patient. The length and flexibility of the catheter body allow the catheter to be inserted into a main vein or artery (typically the femoral artery), directed into the interior of the heart, and then manipulated such that the coagulation electrode contacts the tissue that is to be ablated. Fluoroscopic imaging is used to provide the physician with a visual indication of the location of the catheter.
In some instances, the proximal end of the catheter body is connected to a handle that includes steering controls. Exemplary catheters of this type are disclosed in U.S. Pat. No. 5,582,609. In other instances, the catheter body is inserted into the patient through a sheath and the distal portion of the catheter is bent into loop that extends outwardly from the sheath. This may be accomplished by pivotably securing the distal end of the catheter to the distal end of the sheath, as is illustrated in U.S. Pat. No. 6,071,279. The loop is formed as the catheter is pushed in the distal direction. The loop may also be formed by securing a pull wire to the distal end of the catheter that extends back through the sheath, as is illustrated in U.S. Pat. No. 6,048,329, which is incorporated herein by reference. Loop catheters are advantageous in that they tend to conform to different tissue contours and geometries and provide intimate contact between the spaced tissue coagulation electrodes (or other diagnostic or therapeutic elements) and the tissue.
One lesion that has proven to be difficult to form with conventional devices is the circumferential lesion that is used to isolate the pulmonary vein and cure ectopic atrial fibrillation. Lesions that isolate the pulmonary vein may be formed within the pulmonary vein itself or in the tissue surrounding the pulmonary vein. Conventional steerable catheters and loop catheters have proven to be less than effective with respect to the formation of such circumferential lesions. Specifically, it is difficult to form an effective circumferential lesion by forming a pattern of relatively small diameter lesions. More recently, inflatable balloon-like devices that can be expanded within or adjacent to the pulmonary vein have been introduced. Although the balloon-like devices are generally useful for creating circumferential lesions, the inventors herein have determined that these devices have the undesirable effect of occluding blood flow through the pulmonary vein.
Accordingly, the inventors herein have determined that a need exists generally for structures that can be used to create circumferential lesions within or around bodily orifices without occluding fluid flow and, in the context of the treatment of atrial fibrillation, within or around the pulmonary vein without occluding blood flow.
Accordingly, the general object of the present inventions is to provide a device that avoids, for practical purposes, the aforementioned problems. In particular, one object of the present inventions is to provide a device that can be used to create circumferential lesions in or around the pulmonary vein and other bodily orifices in a more efficient manner than conventional apparatus. Another object of the present invention is to provide a device that can be used to create circumferential lesions in or around the pulmonary vein and other bodily orifices without occluding blood or other bodily fluid flow.
In order to accomplish some of these and other objectives, a probe in accordance with one embodiment of a present invention includes a probe body and a helical structure associated with the distal region of the probe body. In one implementation, a plurality of spaced electrodes are carried by the helical structure. Such a probe provides a number of advantages over conventional apparatus. For example, the helical structure can be readily positioned within the body such that a ring of electrodes is brought into contact with the tissue in or around a pulmonary vein or other bodily orifice. The helical structure also defines an opening that allows blood or other bodily fluids to pass therethrough. As a result, the present probe facilitates the formation of a circumferential lesion without the difficulties and occlusion of blood or other fluids that is associated with conventional apparatus.
In one implementation, the helical structure tapers from a larger proximal diameter down to a smaller distal diameter. The larger diameter will correspond to the pulmonary vein ostium and the smaller diameter will correspond to the interior of the pulmonary vein when the probe is designed to form lesions around a pulmonary vein. So configured, the tapered helical structure will be self-centering when inserted into a pulmonary vein because the structure will wedge itself against the pulmonary vein ostium and the internal wall of the pulmonary vein itself. This insures proper positioning of the electrodes and prevents beating related movement of the heart from the knocking the structure out of position.
The flexibility of the distal portion of the helical structure may be increased and, in some implementations, to a point where the distal portion of the tapered helical structure will be more flexible than the proximal portion. A helical structure with a more flexible distal portion will prevent tissue damage as the physician pokes around within the atrium while attempting to insert the helical structure into a pulmonary vein. The more flexible distal portion is also easily uncoiled for placement within the sheath and will be more likely to remain uncoiled, thereby limiting friction, as it slides though the sheath than will a stiffer distal portion. The stiffer proximal portion, on the other hand, allows the physician to press the electrodes against the tissue with more force so that proper tissue/electrode contact is achieved when lesions are being created.
In one implementation, the probe body and helical structure will be coaxial and arranged such that proximal end of the helical structure will be connected to the probe body by a curved portion that is pre-bent (at, for example, a 45 degree angle) relative to the longitudinal axis of the probe body. The curved portion will typically be bent out of its pre-bent orientation when the helical structure is urged against tissue. As a result, the curved portion will generate a spring force that urges the helical structure against the tissue and improves tissue/electrode contact. Additionally, because the curved portion is located along the axis of the helical structure, the spring force will be distributed evenly around the circumference of the helical structure.
In order to accomplish some of these and other objectives, a probe in accordance with one embodiment of a present invention includes a probe body defining a curved portion having a pre-set curvature and a control element defining a distal portion associated with the distal region of the probe body and extending outwardly therefrom and proximally to the proximal end of the probe body. In one preferred implementation, a plurality of spaced electrodes are carried by the distal region of the probe body and the control element may be used to pull the distal region into a loop that lies in a plane which is angled relative to the longitudinal axis of the probe body (at, for example, 45 degrees). Such a probe provides a number of advantages over conventional apparatus. For example, the curved portion will typically be bent out of its pre-bent orientation when the loop is urged against tissue. As a result, the curved portion will generate a spring force that urges the loop against the tissue and improves tissue/electrode contact.
The above described and many other features and attendant advantages of the present inventions will become apparent as the inventions become better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.